Self-unloading spreaders for materials such as rocks, sand, salt, soil, mulch, and the like are well known. Some are self-powered, such as the spreader disclosed in U.S. Pat. No. 3,235,107 (Tift). Others are meant to be towed and/or powered by another vehicle such as the spreaders disclosed in U.S. Pat. Nos. 3,520,434 (Destefan, et al), 3,037,780 (Skromme et al) and 3,159,296 (Schuitemaker). These spreaders have material moving systems with single power systems such as hydraulics or by the power-take-off of a towing vehicle but not a combination of both. This limits the options an operator of any of these systems has to vary the material spread rate and the throw distance; i.e. the operator can increase these together or decrease these together but not increase/decrease them separately. If the operator provides more power to the spreader to spread more material, the spreader will also throw the material a farther distance from the spreader. If the operator reduces the material flow rate then he also reduces the throw distance.
Another problem conventional spreaders have is they either spread material to both sides of the spreader at once, as does the rotational spreader in U.S. Pat. No. 3,235,107 (Tift), or they are uni-directional and spread material to only one side, as in U.S. Pat. Nos. 3,520,434 (Destefan, et al), 3,037,780 (Skromme et al) and 3,159,296 (Schuitemaker) and 2,786,655 (Cowsert). However, it is often advantageous to be able to spread material to only one side of the spreader at one time and then to be able to spread material to just the other side of the spreader a few moments later without having to totally reposition the spreader. With the spreaders mentioned above, an operator either spreads material to both sides at once, as with the rotational spreader, or would have to turn the entire spreader around to spread material in the other direction, as with the uni-directional spreaders.